A majority of automobiles today utilize airbag crash systems. An airbag is typically located on the steering wheel facing the driver and must be in continuous electrical connection with sensors in the car body. The sensors provide an electrical signal to the airbag crash assembly which instantly inflates the airbag in the event of a crash. Clocksprings are found in virtually every vehicle to electrically connect rotating devices in the steering column to stationary components in other parts of the vehicle.
There are generally two types of clocksprings designs, the coil and the “loop-back” design. In the coil design, long lengths of flat cable (typically 6 to 13 feet) are wrapped around a central hub of a clockspring, in a coil-type fashion. In a loop-back design, a roller and carrier mechanism loop a flat cable (typically 2 to 3 feet) back onto itself inside the clockspring.
In both types of clocksprings, the flat cable comprises a series of parallel conductors sandwiched between two insulating layers of plastic or similar material. The flat cable is terminated by welding the flat cable's conductors to a rigid circuit board or overmolded metallic insert grid.
FIGS. 1A-1C show a prior art flat cable 10 and flat cable termination structure. FIG. 1A shows a rigid circuit board 11 having ten (10) contacts 12 thereon. The contacts 12 are connected to metal conductors 14 traced onto the circuit board 10, which eventually form metal leads 16.
FIGS. 1B and IC show a top and perspective view, respectively, of the flat cable 10 welded to the metal leads 16. The flat cable 10 is generally formed by sandwiching a series of conductors 20 between two insulating layers of plastic or similar material. The insulating layers in FIGS. 1B and 1C are transparent so that the cable conductors 20 can be seen. The insulating layers have an adhesive bonding agent on their interior sides which bond to each other and the cable conductors 20. The ends of the flat cable 10 are stripped to expose the cable conductors 20 therein, which are then welded to the metal leads 16.
The flat cable and flat cable termination structure of the prior art suffers from the disadvantage that it requires the cable conductors 20 and the metal leads 16 to be spaced apart a certain pitch, resulting in larger clocksprings. Additionally, the cable conductors 20 are attached to the contacts 12 via the circuit board 11, adding a structural component between the flat cable 10 and the contacts 12.
In view of the foregoing, it would be advantageous to provide a flexible flat cable for a clockspring having conductors “printed” or “screened” onto a flat cable in order to increase the conductor density (i.e. the amount of conductors in a given space) of the cable. It would further be advantageous to provide a flat cable termination structure which eliminated the circuit board, and directly connected the conductors of the flat cable to the contacts of a connector, thereby eliminating the need for a circuit board or other intermediary connecting device.